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How does overflow affect the security of your code? Explore common dangerous scenarios
In programming, overflow is a worrying safety hazard. Overflow occurs when integer arithmetic attempts to produce a value outside a certain range, which can lead not only to unexpected behavior but also to security vulnerabilities. Although many developers think that the risk of overflow is merely mathematical, it actually has profound implications for the security of your code.
If overflow is not foreseen, the resulting consequences may jeopardize the reliability and security of the program.
The root cause of overflow lies in the processor's register width, which determines the range of values that can be represented. Many modern computers can use multiple-precision arithmetic, which helps avoid overflows, but the fixed width of the registers limits the size of numbers that can be manipulated. For example, the maximum representable value for a 32-bit register is 4294967295, while for a 64-bit register it is 18446744073709551615. When performing arithmetic operations, if the result is outside these ranges, overflow occurs.
Typical overflow scenarios include when dealing with variables like counters, timestamps, and buffer sizes. For example, when you add two integers, suppose the result exceeds the maximum representable value, which causes the counter to wrap around to zero. This could lead to issues such as buffer overflows, which could lead to arbitrary code execution vulnerabilities.
For unsigned integers, modulo wrapping is defined behavior, and the term overflow does not apply.
In some cases, the results of overflow may be foreseeable in certain applications, such as timer and clock operations, where the overflow behavior may be part of the design. However, for most situations, especially in safety-critical environments, such behavior must be carefully considered.
Dangerous example of overflow
The consequences of overflow problems can sometimes be catastrophic. Historically, the Therac-25 radiation therapy machine caused at least six deaths from radiation overdose due to unhandled arithmetic overflow. The main failure during the first launch of the Ariane 5 rocket in 1996 was due to an overflow in the engine's steering control software, which caused the rocket to quickly disintegrate.
Overflow is considered a common cause of failure in many programming errors.
Overflow can also cause interesting behavior in some computer games. For example, in Super Mario Bros., when the player reaches 128 lives, the life counter wraps around to zero, causing the game to end. In Donkey Kong, the time calculation overflow trapped the player in a certain level, unable to progress.
How to deal with overflow
To prevent overflow issues, developers can take several approaches to detect, avoid, and handle overflow.
Detection
Runtime overflow detection is an important safeguard. Some languages, such as Java, provide special methods to throw overflow exceptions. For C/C++, you can use the Undefined Behavior Checker (UBSan) to help identify potential overflow errors.
Avoid
Using a sufficiently large data type in variable declarations ensures that overflow is avoided. Even if the internal logic is not simple, effective order of operations and operand checking can help prevent overflows.
Processing
If overflow is expected to occur, the application can insert a test to check whether overflow has occurred and decide the next action based on the result of the check. For example, if a result from user input overflows, action should be taken to stop program execution rather than allowing the program to continue using erroneous data, which could result in a more serious failure.
Many development languages now provide functions to handle overflow problems. For example, Rust, in addition to basic mathematical operations, also provides a variety of ways to choose how to handle overflow, including wrapping, saturation, or throwing exceptions. . This design provides developers with a better choice between security and performance.
Ultimately, overflow is not a technical issue per se, but a quality mark that programmers trust in their application. For developers, how to effectively prevent overflow problems to ensure the security of program code will always be an important issue, especially in the current increasingly complex network world. We should think about how future programming languages will further improve their ability to handle overflow problems?
